Apparatus for the electrolysis of alkali metal chloride solutions with mercury cathode

ABSTRACT

AN APPARATUS FOR THE ELECTROLYSIS OF ALKALI METAL CHLORIDE SOLUTIONS WITH MERCURY CATHODE. FRESH BRINE IS DELIVERED THROUGH A HOLLOW SHAFT AND UNIFORMLY DISTRIBUTED TO A PLURALITY OF PASSAGES IN THE ANODE. SMALL OPENINGS IN THE PASSAGES ON THE ACTIVE SIDE OF THE ANODE ENABLE BRINE TO PASS INTO THE NARROW ELECTROLYSIS GAP BETWEEN THE ANODE AND MERCURY CATHODE. SMALL OPENINGS IN THE SOLID PART OF THE ANODE OR BETWEEN THE PASSAGES ENABLE THE WEAKENED BRINE CHARGED WITH SMALL CHLORINE GAS BUBBLES TO FLOW INTO THE CELL CHAMBER.

July 17, 1973 F. GLOS ETAL 3,746,631

APPARATUS FOR THE ELECTROLYSIS OF ALKALI METAL CHLORIDE SOLUTIONS WITHMERCURY CATHODF OriginalFiledJan. 10, 1969 6 Sheets-Sheet 1 INVENTORSFame: GLOS JoAcmM M'ISCHPRE July 17, 1973 F. GLOS ETAL 3,746,631

APPARATUS FORT-H11 ELECTROLYSIS 0F ALKALl METAL CHLORIDE SOLUTIONS WITHMERCURY CATHODE Original Filed Jan. 10, 1969 6 Sheets-Sheet 2ooooooooowj (@oo INVENTORS FRANZ. GLOS dmcum \A CHKE y 17, 1973 F. GLOSETAL 3,746,631

I APPARATUS FOR THE ELECTROLYSIS OF ALKALI METAL CHLORIDE SOLUTIONS WITHMERCURY CATHODE Original Filed Jan. 10, 1969 6 Sheets-Sheet 3;

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7 v APPARATUS FOR THE ELECTROLYSIS OF ALKALI METAL CHLORIDE SOLUTIONSWITH MERCURY CATIIODE Original Filed Jan. 10, 1969 6 Sheets-Sheet 6INVENTORS Fmwz GLOS JoAcHm SCHKE m A' YORKEV United States PatentAPPARATUS FOR THE ELECTROLYSIS OF ALKALI mTAL OHLORIDE SOLUTIONS WITHMERCURY CATHODE Franz Glos, Salzgitter-Lebenstedt, and Joachim Mischke,Dortmund-Hochsten, Germany, assignors to Friedrich Uhde GmbH, Dortmund,Germany Original application Jan. 10, 1969, Ser. No. 790,337, nowabandoned. Divided and this application Aug. 26, 1971, Ser. No. 175,066

Int. Cl. Btllk 3/04; C22d 1/04 US. Cl. 204-219 2 Claims ABSTRACT OF THEDISCLOS An apparatus for the electrolysis of alkali metal chloridesolutions with mercury cathode. Fresh brine is delivered through ahollow shaft and uniformly distributed to a plurality of passages in theanode. Small openings in the passages on the active side of the anodeenable brine to pass into the narrow electrolysis gap between the anodeand mercury cathode. Small openings in the solid part of the anode orbetween the passages enable the weakened brine charged with smallchlorine gas bubbles to flow into the cell chamber.

CROSS-REFERENCE TO RELATED APPLICATION This application constitutes adivision of application, Ser. No. 790,337, filed Jan. 10, 1969, entitledMethod and Apparatus for the Electrolysis of Alkali Metal ChlorideSolutions with Mercury Cathode (now abandoned).

BACKGROUND OF THE INVENTION In the electrolysis of an alkali metalchloride solution with utilization of a mercury cathode, the aim is todecrease the costs of an electrolysis installation in this way, that thecurrent density is increased and the floor space of the electrolyticcell is held as small as possible. By means of high cathodic currentdensity, the loss as a result of reduction of the chlorine formed on theanode and the re-formation of alkali chloride is lessened and therebythe electrolytic efiiciency is improved.

High electric current density has as a result a high gas productionspeed per surface entity of the active anode surface. The bubbles ofchlorine gas then become so small, that their diameter amounts to lessthan 0.1 mm. and their rising speed lies in the Stokes range. The liftor buoyancy of the gas bubbles then is no longer sufiicient to removethe bubbles from the anode surface. The small gas bubbles are verystable and combine with difiiculty into larger bubbles. They remaindispersed in the electrolytes, are by means of local circulation of thebrine entrained or pulled along again into the intermediary space of theanode and the cathode and form together with the newly occurring gas afoam which prevents the passage or flow of current by means of itsinsulating effect and causes in this way an increase in the cell tensionand a greater expenditure of energy.

It has been suggested that in order to facilitate the movement of thegas bubbles away from the active anode surface, inclined cathode andanode surfaces and/or grooved and perforated anode plates may beemployed.

By means of coarse perforation of the anode plates, as for examplesuggested in the US. Pat. No. 3,308,043, probably for larger gasbubbles, the ascending path may 3,746,631 Patented July 17, 1973 beshortened. However, an appreciable part of the active anode surface islost in this manner.

By means of the differentiated structure of the active anode surface,there results a non-uniform current distribution. The very small gasbubbles, which occur with a particularly high current density andcontribute to the formation of foam have, however, an ascending speed sosmall that through a construction of this type, no essential advantageis achieved.

SUMMARY OF THE INVENTION The object of this invention is to produce anapparatus through which, with similar cell size, a larger output ofcells is secured. The increase in the current density required for thepurpose with similar or smaller cell tension may be attained in the mosteffective way by means of a change in the flow conditions in thereaction chamber between anode and cathode. The apparatus ischaracterized in that fresh brine is conveyed to the area of eachindividual anode plate and is uniformly distributed over the activeanode surface facing the reaction chamber. An apparatus is producedwhich is characterized by at least one hollow anode shaft per anode,which is connected with numerous cavities disposed in the anode plate,the walls of said cavities having on the active side of the anode platenumerous small openings. Through the hollow shaft of the anode freshbrine is supplied and is distributed in the cavities of the anode plateover the entire anode surface, and then passes out through numeroussmall holes in the active anode surface into the reaction chamberbetween anode and cathode.

In order that not all gas bubbles forming in the reaction chamber musttravel over a large part of the active anode surface up to the edge ofthe anode plate for escaping from the reaction chamber, it is ofadvantage to provide the anode at the non-hollow places in the anodeplate likewise with numerous small holes, through which gas bubbles mayescape before the fresh brine subsequently flows into the upper cellchamber.

The direct feed of the fresh brine into the reaction chamber and theshort path for the formed gas bubbles insure the energizing of theelectrolysis cell according to the invention with high current densityat low voltage drop, so that the electrolytic efiiciency issubstantially increased.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectionalelevation of an electrolysis cell showing a reaction chamber containinga mercury cathode and an anode plate, the foam from the chamber beingd-egasified in a separator which is diagrammatically shown;

FIG. 2 is a vertical sectional view of the anode plate assembly taken onthe line 2-2 of FIG. 3;

FIG. 3 is a top plan view of the anode plate assembly shown in FIG. 1;

FIG. 4 is a vertical sectional view of an alternate form of anode plateassembly in which both the top and bottom plate members are profiled andtaken on the line 44 of FIG. 5;

FIG. 5 is a fragmentary top plan view of an alternate form of anodeplate assembly shown in FIG. 4;

FIG. 6 is a fragmentary bottom plan view of the anode plate shown inFIG. 5;

FIG. 7 is a vertical sectional view on the line 77 of FIG. 8 of analternate form of anode plate assembly in which the pipes are flattenedon the underside, the upper side being dome-shaped in cross section;

FIG. 8 is a fragmentary top plan view of the form shown on FIG. 7;

FIG. 9 is a sectional view substantially on the line 99 of FIG. 8;

FIG. 10 is a vertical sectional view on the line 10-10 of FIG. 11showing an alternate form of anode plate assembly in which the pipes arerectangular in cross section;

FIG. 11 is a fragmentary top plan view of the form shown on FIG. 10;

FIG. 12 is a sectional view substantially on the line 12-12 of FIG. 11;

FIG. 13 is a vertical sectional view on the line 1313 of FIG. 14 showingan alternate form somewhat similar to that shown on FIGS. 10 to 12 butin which current is supplied to the anode plate through guide rails;

FIG. il4 is a fragmentary top .plan view of the form shown in FIG. 13;and

FIG. 15 is a sectional view of the guide rails and a rectangular pipe,the parts connected to the upper rail being removed.

DESCRIPTION OF PREFERRED EMBODIMENTS The electrolysis installation isshown diagrammatically by way of example in FIG. 1. Fresh brine suppliedto the anode within a closed chamber 4a through a centrally disposedtube 1 made of titanium, distributes itself at the foot radially intothe cavities 2 of the anode plate and enters through the bores 3 intothe narrow electrolysis gap between anode and the mercury cathode withinthe chamber 4a. The weakened brine flows out charged with small chlorinegas bubbles through bores 4 into the cell chamber. This foam leaves thecell through tuyeres 5 and is degasified in a separator 6 by means ofdropwise addition of diluted hydrochloric acid at 9. The anolyte flowsthrough feed pipes 7 downwardly and the chlorine gas escapes upwardlythrough feed pipes 8.

In order to distribute the fresh brine for an entire cell uniformly inthe individual anodes, each anode brine feed has connected in front anozzle 11. The current is supplied through a copper tube 10, which isprotected on the outside by a pipe made of titanium or a temperature andchlorine resistant synthetic material. The mercury flows in direction ofthe rows of holes in the anode plate, the brine flowing transversely tothis direction.

The anode consists of metal, preferably of titanium, whose activesurface is covered with a coating layer protecting against passivationand amalgamation. The inner surfaces of the anode cavities must likewisebe passivated. All bores and slots in the anodes are rounded off on thelower side in order to prevent an increased current density at thesepoints, which may have as a result a destruction or corrosion of theprotective covering layer. The hollow anode plate not only aflfords goodbrine distribution, but also a good current distribution withoutnoteworthy decrease in voltage, which would cause a nonuniform currentdensity.

Prerequisite for the utilization of the methods according to theinvention is a large quantity of brine with reference to acorrespondingly high brine speed in the dissociation or decompositionchamber between anode and cathode for washing away the gas bubbles andfor the formation of a foam with flow tendency. The progress must bewith low weakening, that is, instead of 35 grams per liter according tothe conventional method, with a weakening of approximately 5 grams perliter with a specific load of ka./m. Per cm. anode surface and secondsthere result according to Faraday 0.00106 grams of chlorine gas, whichcorresponds with moist chlorine of approximately 75 C. to a volume of0.59 cm. second. For 1 ton of chlorine there was required 1.7 tons NaCl,

so that with 5 g./l. weakening 0.36 cm? brine/sec. cm. anode surface arerequired. The mixture flowing out of the anode amounts then to 0.59 plus0.36:0.95 emfi/ sec. cm. The portion of gas in the foam is accordingly62%. The specific weight of the foam amounts accordingly to even 0.46kp./l. as compared with about 1.2 kp. of the brine. With an electrodegap of about 0.5 mm. a brine speed sets in, in the dissociation chamberof about 0.3 m./sec.

A form of anode structure is shown on FIGS. 2 and 3 in which a rigid,level plate 14 made of titanium is welded to a profiled pressed titaniumplate 15. The rim is continuously welded and in the grooves the upperplate 15 is joined at the points of bores 4 with the lower plate 14 bymeans of spot welding. In the center of the plate is seated a tuyere 16made of titanium, which is connected with a pipe 1 by screwthreads orwelding. Its outer circumference carries threads, on which a copper pipe10 is screwed for the current feed. The pipe 10 is protected on theoutside against attack by moist chlorine by means of a casing 17.Between the plate 15 and the pipe 10 is disposed a packing 18, which istightened by means of the screwed on copper pipe 10.

In the center of the anode plate below the anode shaft the bores 4cannot be disposed in the same arrangement. The bores 4 disposed next tothe center must be dimensioned somewhat larger in diameter, so that thebubbles developed in the center may pass with the brine into the uppercell chamber.

FIGS. 4 to 6 show an anode construction with pressed plates 19 and 20 oftitanium profiled on both sides, which are welded together at the rim.At the points of the bores 4 the plates 19 and 20 are connected in thegrooves 22 by means of spot welding. The groove shaped depressions onthe lower side of the anode plate are continuous, while the depressionson the upper side, in the center and through the brine distributionstrips 21 lying transversely to the direction of mercury flow areinterrupted. This construction has the advantage that the continuousdepressions in the center bring about a better carrying away of thefoam.

FIGS. 7, 8 and 9 show a further anode construction, which is composed ofpipes 23 made of titanium rounded at their upper sides and flattened ontheir lower side 5. The pipes are connected in the center with a pipe24' having a transversely disposed brine and current distribution pipepart 24. For good brine distribution to all pipes, the inlet openings 23disposed in the center on the pipes are made so small that they act asnozzle. The pipes 23 are inserted in and welded to curved recesses 26'in the distribution pipe part 24. The pipe 24' has a cover plate 25welded or soldered to the pipe part 24. The brine foam may escape fromthe reaction chamber through gaps 26 between the pipes in the upper cellchamber. Holes or bores 3 in the flat side of each pipe 23 enables brineto flow to the gap between the anode and mercury cathode.

FIGS. 10 to 12, as well as FIGS. 13 to 15, show similar anodeconstructions, only with the difference, that instead of the flattenedpipes 23, rectangular pipes 27 are utilized. With the anode according toFIGS. 13 to 15, the current is supplied to the anode plate throughcurrent guide rails 28 and 29. By means of this arrangement of rails, astill better current distribution is secured over the anode surface.

What we claim is:

1. Apparatus for the electrolysis of alkali metal chloride solution inwhich a reaction chamber is arranged between an anode and a mercurycathode, said apparatus comprising an anode structure in the form ofsuperposed plates of electrical conductive material, one of said platesbeing profiled to provide hills and valleys, a welded connection betweensaid plates at the rim portions, the valleys of said profiled plateengaging the other plate, welded connections between said plates at thejunction of said valleys, apertures through said valleys and said other5 plate for the escape of depleted brine and gaseous chlorine from thereaction chamber, the hills providing with said other plate ducts forthe passage of fresh brine, holes in said other plate in the region ofsaid hills for the passage of fresh brine to the reaction chamber, anupstand- 5 ing tube extending from the central portion of said anodestructure through which fresh brine is supplied to said ducts, and anelectrically conductive pipe outside of said tube and through whichelectric current is delivered to said anode structure.

2. Apparatus as claimed in claim 1, in which both plates are profiled toprovide box-like channel elements disposed in spaced generally parallelrelation.

6 References Cited UNITED STATES PATENTS 3,535,223 10/1970 Baecklund eta1. 204284 X 3,507,771 4/1970 Donges et al. 204284 X JOHN H. MACK,Primary Examiner D. R. VALENTINE, Assistant Examiner US. Cl. X.R.

